[feature] scheduled statuses (#4274)

An implementation of [`scheduled_statuses`](https://docs.joinmastodon.org/methods/scheduled_statuses/). Will fix #1006.

this is heavily WIP and I need to reorganize some of the code, working on this made me somehow familiar with the codebase and led to my other recent contributions
i told some fops on fedi i'd work on this so i have no choice but to complete it 🤷‍♀️
btw iirc my avatar presents me working on this branch

Signed-off-by: nicole mikołajczyk <git@mkljczk.pl>
Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4274
Co-authored-by: nicole mikołajczyk <git@mkljczk.pl>
Co-committed-by: nicole mikołajczyk <git@mkljczk.pl>

internal/api/client/scheduledstatuses/scheduledstatusget.go

@@ -0,0 +1,98 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package scheduledstatuses
+
+import (
+	"net/http"
+
+	apiutil "code.superseriousbusiness.org/gotosocial/internal/api/util"
+	"code.superseriousbusiness.org/gotosocial/internal/gtserror"
+
+	"github.com/gin-gonic/gin"
+)
+
+// ScheduledStatusGETHandler swagger:operation GET /api/v1/scheduled_statuses/{id} getScheduledStatus
+//
+// Get a scheduled status with the given id.
+//
+//	---
+//	tags:
+//	- scheduled_statuses
+//
+//	produces:
+//	- application/json
+//
+//	parameters:
+//	-
+//		name: id
+//		type: string
+//		description: ID of the status
+//		in: path
+//		required: true
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- read:statuses
+//
+//	responses:
+//		'200':
+//			schema:
+//				"$ref": "#/definitions/scheduledStatus"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'404':
+//			description: not found
+//		'406':
+//			description: not acceptable
+//		'500':
+//			description: internal server error
+func (m *Module) ScheduledStatusGETHandler(c *gin.Context) {
+	authed, errWithCode := apiutil.TokenAuth(c,
+		true, true, true, true,
+		apiutil.ScopeReadStatuses,
+	)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	targetScheduledStatusID, errWithCode := apiutil.ParseID(c.Param(apiutil.IDKey))
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	scheduledStatus, errWithCode := m.processor.Status().ScheduledStatusesGetOne(
+		c.Request.Context(),
+		authed.Account,
+		targetScheduledStatusID,
+	)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	apiutil.JSON(c, http.StatusOK, scheduledStatus)
+}